SUSTAINABLE UTILISATION OF TABLE MOUNTAIN GROUP AQUIFERS Anthony A. Duah

182 Pages·2011·5.38 MB·English

SUSTAINABLE UTILISATION OF TABLE MOUNTAIN GROUP
AQUIFERS

Dissertation submitted to the University of the Western Cape in the fulfillment of the
requirements for the degree of
Doctor of Philosophy

By

Anthony A. Duah

In the
Department of Earth Sciences
Faculty of Natural Sciences
University of the Western Cape
Cape Town

Supervisor: Prof. Yongxin Xu

July, 2010
DECLAR  ATION

I declare that SUSTAINABLE UTILISATION OF TABLE MOUNTAIN GROUP AQUIFERS

is my own work, that it has not been submitted for any degree or examination in any other

University, and that all the sources I have used or quoted have been indicated and acknowledged
by complete references.

Full Name: Anthony Appiah Duah Date: July, 2010

Signed…………………………………..
ABSTRACT

Sustainable Utilisation of Table Mountain Group Aquifers

A. Duah
PhD Thesis
Department of Earth Sciences

Key words: Sustainability, sustainable yield, safe yield, aquifer, Climate Change, Climate
Variability, trend analysis, recharge, discharge, adaptive management, dependent ecosystem,
hydrostratigraphic unit, precipitation index.

The Table Mountain Group (TMG) Formation is the lowest member of the Cape Supergroup
which consists of sediments deposited from early Ordovician to early Carboniferous times,
approximately between 500 and 340 million years ago. The Table Mountain Group (TMG)
aquifer system is exposed along the west and south coasts of South Africa. It is a regional
fractured rock aquifer that has become a major source of bulk water supply to meet the
agricultural and urban water requirements of the Western and Eastern Cape Provinces of South
Africa. The TMG aquifer system comprises of an approximately 4000 m thick sequence of
quartz arenite and minor shale layers deposited in a shallow, but extensive, predominantly east-
west striking basin, changing to a northwest orientation at the west coast. The medium to coarse
grain size and relative purity of some of the quartz arenites, together with their well indurated
nature and fracturing due to folding and faulting in the fold belt, enhance both the quality of the
groundwater and its exploitation potential for agricultural and domestic water supply purposes
and its hot springs for recreation. The region is also home to some unique and indigenous floral
species (fynbos) of worldwide importance. These and other groundwater dependent vegetation
are found on the series of mountains, mountain slopes and valleys in the Cape Peninsula. The
hydrogeology of the TMG consists of intermontane and coastal domains which have different
properties but are interconnected. The former is characterized by direct recharge from rain and
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snow melt, deep groundwater circulation with  hot springs and low conductivity groundwater.
The coastal domain is characterized by shallow groundwater occurrence usually with moderate

to poor quality, indirect recharge from rainfall of shallow circulation and where springs occur

they are usually cold.

The sustainable utilization of the TMG aquifer addressed the issues of the groundwater flow
dynamics, recharge and discharge to and from the aquifer; challenges of climate change and
climate variability and their potential impact on the aquifer system. The concept of safe yield,
recharge and the capture principle and the integration of sustainable yield provided the basis for
sustainable utilization with the adaptive management approach. Methodology used included the
evaluation of recharge methods and estimates in the TMG aquifer and a GIS based water balance
recharge estimation. The evaluation of natural discharges and artificial abstractions from the
TMG aquifer system as well as its potential for future development. The Mann-Kendal trend
analysis was used to test historical and present records of temperature and rainfall for significant
trends as indication for climate variability and change. The determination of variability index of
rainfall and standard precipitation index were additional analyses to investigate variability. The
use of a case study from the Klein (Little) Karoo Rural Water Supply Scheme (KKRWSS)
within the TMG study area was a test case to assess the sustainable utilization of TMG aquifers.

Results show that recharge varies in time and space between 1% and 55% of MAP as a result of
different hydrostratigraphic units of the TMG based on geology, hydrology, climate, soil,
vegetation and landuse patterns however, the average recharge is from 1% to 5% of MAP. The
TMG receives recharge mainly through its 37,000 km2 of outcrop largely exposed on
mountainous terrain. Natural discharges from the TMG include 11 thermal and numerous cold
spring discharges, baseflow to streams and reservoirs, and seepage to the ocean. Results from
this study also show increasing temperature trend over the years while rainfall trend generally
remain unchanged in the study area. Rainfall variability persists hence the potential for floods
and droughts in the region remain. Global and Regional Models predict about 10% to 25%
reduction in rainfall and increase in variability in future. Impacts of this change in climate will
affect the different types of aquifers in various ways. Increase in temperature and reduction in
rainfall will increase evapotranspiration, reduce surface flows and eventually reduce shallow
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aquifer resources. Coastal aquifers risk upsurge i n salinisation from sea level rise and increase in
abstractions from dwindling surface water resources. While floods increase the risk of

contamination to shallow aquifers droughts put pressure on all aquifers especially deep aquifers

which are considered to be more reliable due to the fact that they are far removed from surface

conditions. Future population growth and increase in freshwater demand will put more pressure
on groundwater.
Recharge to groundwater have been over-estimated in certain areas in the past leading to high
abstraction rates from boreholes causing extensive groundwater storage depletion evident by
high decline in groundwater levels in these areas and hampering sustainable management of the
aquifer resources. Over-abstraction have resulted in loss of stream flow and baseflow reduction
to streams during summer, complete loss of springs and reduction of flow to others. Flow to
wetlands, riparian vegetation, and sometimes loss and shifts in dependent ecosystems have also
resulted from over-abstraction. Sustainability has spatial and temporal implications due to
changing climate and demand.

The study recommends adaptive management practices in which several factors are considered in
managing groundwater together with surface water resources in order to maintain ecological and
environmental integrity. The KKRWSS and other groundwater supply schemes in the Western
and Eastern Cape Provinces demonstrate the huge potential of the TMG to provide freshwater
supply for domestic and irrigation water needs however, the huge decline in groundwater levels
due to over-abstraction in the KKRWSS and other groundwater schemes underscores the need
for sustainable utilization of the TMG groundwater resources for present and future generations
with minimal impacts on the quality, dependent hydrological and ecosystems as well as the
environment.

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ACKNOWLE DGEMENTS

This work has been as a result of the help and cooperation of many individuals and institutions.

The author would like to express his heart-felt gratitude to the following persons who contributed

in no small way to the successful completion of this thesis. Those who need special mention
include:
 Professor Yongxin Xu who gave me the opportunity to undertake this exercise and
guided me throughout the period of the study with direction and useful advice.
 Professors Niko Verhoest, Luc Brendonck, Lincoln Rait and Eberhard Braune for your
pieces of advice and help.
 The VLIR (Flemish Inter University Council) programme of the University of the Western
Cape for granting me the scholarship during the first three years of this study.
 The staff of the Department of Earth Sciences of UWC especially Caroline Barnard who
was my first call and Wasielah Davids for the help in assisting me throughout the study.
 Professor Jonathan Levy for his invaluable assistance during his time at UWC.
 The Department of Water Affairs in Bellville and Pretoria, Mike Smart, Henry De Haast,
Roseeda Peters, Chaka Shouneez and Arul Uz-Zaman for providing me with lots of data
for this study.
 The Water Research Commission for all the reports you freely provided.
 All the friends and colleagues I met at the Department during my time of studies
including Jaco Nel, Humberto Saeze, Riyaz Nakhwa, Segun Adelana, Lixiang Lin, Haili
Jia, Wisemen Chingombe, James Ayuk, Opuwari Mimonitu, Solomon Adekola,
Thokozani Kanyerere, Josue Bahati, Zayed Brown, Innocent Muchingani and all the
many MSc and honors students who shared friendship with me during my stay in UWC.
 Special posthumous thanks to Patrick Ackon (RIP) for his assistance in helping me find
my way around in and out of campus during my first few months in South Africa. Also to
Professor Francis Benyah, Yaw Nkansah-Gyekye, Samuel Kwofie, Francis Adu-Poku
(RIP), colleagues from Ghana who were always there to help and offer friendship.
 CSIR Water Research Institute, Ghana (my employers), who gave me the time and
assistance to pursue this degree.
 My family for the patience, support and encouragement all the time I was away from
home pursuing this degree.
May the Lord bless and multiply back to you what you gave me. I am grateful to you all.

Anthony A. Duah.
Cape Town.

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Table of Content

Page

Table of Content ............................................................................................................................ v

List of Figures ................................................................................................................................ x
List of Tables ............................................................................................................................... xii
List of Appendices ...................................................................................................................... xiii
CHAPTER 1 INTRODUCTION ................................................................................................. 1
1.1 Background of study ........................................................................................................ 1
1.2 Objectives of the study ..................................................................................................... 3
1.3 Literature Review ............................................................................................................. 3
1.3.1 The Concept of Sustainability and Safe Yield .......................................................... 3
1.3.2 Recharge, Sustainability and the Capture Principle .................................................. 4
1.3.3 Sustainability and Sustainable Pumping Rates ......................................................... 9
1.3.4 Sources of water to pumping wells and basin sustainable yield ............................. 11
CHAPTER 2 DEFINITION AND APPROACH TO GROUNDWATER SUSTAINABLE
YIELD …………………………………………………………………………………..15
2.1 The American Concept of Groundwater Sustainable Yield ........................................... 15
2.1.1 The spatial and temporal aspects of sustainable yield ............................................ 15
2.1.2 Understanding the boundaries of the system and water needs ............................... 16
2.1.3 Adaptive management ............................................................................................ 16
2.2 The Australian Concept of Sustainable Yield ................................................................ 17
2.2.1 Extraction regime .................................................................................................... 18
2.2.2 Acceptable levels of stress ...................................................................................... 18
2.2.3 Storage depletion .................................................................................................... 19
2.2.4 Protecting dependent economic, social and environmental values ......................... 19
2.3 The South African Approach to Sustainable Yield ........................................................ 20
2.3.1 Resource Directed Measures (RDM) ...................................................................... 20
2.3.2 Groundwater use and adaptive management .......................................................... 22
2.3.3 The TMG Aquifer System and Sustainable Yields ................................................. 23
2.4 Methodology .................................................................................................................. 27
2.4.1 Methodology in determining sustainability ............................................................ 27
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2.4.2 Data Requirements ......................... ......................................................................... 28
2.4.2.1 Precipitation data ............................................................................................. 30

2.4.2.2 Water levels and borehole information data .................................................... 30

2.4.2.3 Temperature data ............................................................................................. 30

2.4.2.4 Other data and information .............................................................................. 30
2.5 Summary ........................................................................................................................ 31
CHAPTER 3 HYDROGEOLOGICAL SETTING OF THE TMG .......................................... 32
3.1 History and Lithostratigraphy ........................................................................................ 32
3.2 Structure ......................................................................................................................... 35
3.3 Geomorphology and Drainage ....................................................................................... 37
3.4 Hydrogeological Domains.............................................................................................. 38
3.5 Aquifer types and characteristics ................................................................................... 39
3.6 Occurrence of Springs .................................................................................................... 41
3.7 Porosity, Storativity and Transmissivity ........................................................................ 43
3.7.1 Porosity ................................................................................................................... 43
3.7.2 Storativity ................................................................................................................ 45
3.7.3 Transmissivity ......................................................................................................... 46
3.8 Groundwater Quality in the TMG .................................................................................. 47
3.8.1 Hydrochemical characteristics ................................................................................ 47
3.8.2 Isotope analysis of deep borehole and hot springs.................................................. 50
3.8.3 Problems associated with TMG groundwater ......................................................... 51
CHAPTER 4 GROUNDWATER FLOW DYNAMICS IN THE TMG ................................... 52
4.1 Aquifer Recharge to the TMG ....................................................................................... 52
4.1.1 The Conceptual recharge model ............................................................................. 52
4.1.2 Recharge Mechanisms ............................................................................................ 53
4.1.3 Spatial and temporal variability of recharge ........................................................... 54
4.1.4 Selection of Recharge methods ............................................................................... 55
4.1.4.1 Hydrostratigraphic regions of the TMG .......................................................... 56
4.1.4.2 Commonly used recharge methods in Southern Africa ................................... 57
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4.1.4.3 Recharge forecasting .............. ......................................................................... 59
4.1.5 Recharge Estimation in the TMG .. ......................................................................... 59
4.1.6 Regional Water Balance in the TMG ...................................................................... 61

4.1.6.1 Components of the water balance model ......................................................... 63

4.2 Aquifer Discharges from the TMG ................................................................................ 69
4.2.1 Natural discharges from the TMG aquifer .............................................................. 70
4.2.1.1 Baseflow in the TMG ...................................................................................... 70
4.2.1.2 Spring flow in the TMG .................................................................................. 71
4.2.1.3 Discharge to other water bodies ...................................................................... 71
4.2.2 Artificial discharges from TMG ............................................................................. 72
4.2.2.1 Borehole abstractions from TMG .................................................................... 72
4.2.3 Groundwater Dependent Ecosystems ..................................................................... 74
4.2.3.1 Level of Dependency and Threats to GDEs .................................................... 76
4.2.3.2 The Presence of GDEs in the TMG ................................................................. 77
4.3 Summary ........................................................................................................................ 78
CHAPTER 5 CLIMATE VARIABILITY AND ITS IMPACT ON GROUNDWATER ........ 80
5.1 Introduction .................................................................................................................... 80
5.2 Historical Climate Trends in Southern Africa................................................................ 81
5.2.1 Climate patterns in the South Western Cape .......................................................... 82
5.2.2 Global temperature changes .................................................................................... 83
5.3 Trend Analysis ............................................................................................................... 85
5.3.1 The Mann-Kendall (M-K) trend test ....................................................................... 85
5.3.2 Temperature trends in South Africa ........................................................................ 87
5.3.3 Current temperature trends in the Western Cape .................................................... 88
5.3.4 Precipitation trends ................................................................................................. 89
5.3.4.1 Basic statistics.................................................................................................. 90
5.3.4.2 Autocorrelation function .................................................................................. 92
5.3.5 Current precipitation trends in the Western Cape ................................................... 92
5.3.6 Rainfall Variability ................................................................................................. 95
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5.4 The Standard Precipitation Index .......... ......................................................................... 98
5.4.1 SPI and groundwater fluctuations .. ....................................................................... 104
5.4.2 Time Lag between Rainfall and Recharge ............................................................ 111

5.5 The Response of Groundwater Flow Dynamics to Climate Change and Variability .. 113

5.5.1 Impacts on Shallow Aquifers ................................................................................ 115
5.5.2 Impacts on Coastal Aquifers ................................................................................. 116
5.5.3 Impacts on Deep Aquifers .................................................................................... 117
5.5.4 Timing of Recharge and Aquifer Properties ......................................................... 117
5.6 Summary ...................................................................................................................... 118
CHAPTER 6 SUSTAINABLE UTILISATION OF GROUNDWATER RESOURCES – A
CASE STUDY OF THE KLEIN KAROO RURAL WATER SUPPLY SCHEME
(KKRWSS). ....................................................................................................................... 121
6.1 Introduction .................................................................................................................. 121
6.2 Background of the KKRWSS Study Area ................................................................... 122
6.2.1 Topography and Drainage ..................................................................................... 122
6.2.1.1 Spring flows ................................................................................................... 124
6.2.2 Climate .................................................................................................................. 124
6.2.3 Geology and hydrogeological setting of the Kammanassie Mountain area ......... 125
6.2.4 Wellfields .............................................................................................................. 126
6.2.5 Properties of the TMG aquifer in the KKRWSS .................................................. 128
6.2.6 Recharge Estimates of the Vermaaks River wellfield .......................................... 129
6.3 Problems Associated with the KKRWSS Project ........................................................ 129
6.3.1 Decline of water levels.......................................................................................... 130
6.3.1.1 Abstraction management of the Vermaaks wellfield .................................... 134
6.3.2 Iron clogging and changes in water quality .......................................................... 135
6.3.3 Drying up of springs and impact on vegetation and ecosystems. ......................... 137
6.4 Sustainable management approach to Scheme problems ............................................. 138
6.4.1 Stabilization of water levels .................................................................................. 138
6.4.2 Managing Iron clogging and water quality problems ........................................... 139
6.4.3 Management of spring losses ................................................................................ 140
6.5 Summary ...................................................................................................................... 141
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